<template>
  <div class="spec-preview">
    <img :src="defaultImg.imgUrl"/>
    <div class="event" @mousemove="move"></div>
    <div class="big">
      <img :src="defaultImg.imgUrl" ref="bigImg"/>
    </div>
    <div class="mask" ref="mask"></div>
  </div>
</template>

<script>
export default {
  name: "Zoom",
  data() {
    return {
      defaultIndex: 0
    }
  },
  props: ['imageList'],
  mounted() {
    this.$bus.$on('changeDefaultIndex', (index) => {
      this.defaultIndex = index
    })
  },
  computed: {
    defaultImg() {
      return this.imageList[this.defaultIndex] || {}
    }
  },
  methods:{
    move(event){
      //第一步 鼠标动 蒙版动
      //计算蒙版的位置
      let mask=this.$refs.mask
      let bigImg=this.$refs.bigImg
      //第二步 算鼠标的位置
      let mouseX=event.offsetX
      let mouseY=event.offsetY
      let maskX=mouseX-mask.offsetWidth/2
      let maskY=mouseY-mask.offsetHeight/2
      //在赋值之前计算一下边界
     if (maskX<0){
       maskX=0
     }else if (maskX>mask.offsetWidth){
       maskX=mask.offsetWidth
     }
     if (maskY<0){
       maskY=0
     }else if (maskY>mask.offsetHeight){
       maskY=mask.offsetHeight
     }
      mask.style.left=maskX+'px'
      mask.style.top=maskY+'px'
      //第三步 蒙版动 大图动
      bigImg.style.left=-2*maskX+'px'
      bigImg.style.top=-2*maskY+'px'

    }
  }
}
</script>

<style lang="less">
.spec-preview {
  position: relative;
  width: 400px;
  height: 400px;
  border: 1px solid #ccc;

  img {
    width: 100%;
    height: 100%;
  }

  .event {
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    z-index: 998;
  }

  .mask {
    width: 50%;
    height: 50%;
    background-color: rgba(0, 255, 0, 0.3);
    position: absolute;
    left: 0;
    top: 0;
    display: none;
  }

  .big {
    width: 100%;
    height: 100%;
    position: absolute;
    top: -1px;
    left: 100%;
    border: 1px solid #aaa;
    overflow: hidden;
    z-index: 998;
    display: none;
    background: white;

    img {
      width: 200%;
      max-width: 200%;
      height: 200%;
      position: absolute;
      left: 0;
      top: 0;
    }
  }

  .event:hover ~ .mask,
  .event:hover ~ .big {
    display: block;
  }
}
</style>